1. Field of the Invention
This invention relates to a fuel supply control system for use in internal combustion engine such as gasoline engines, diesel engines, or the like and, more particularly, to such a fuel supply control system utilizing a digital computer for determining an optimum pulse width of fuel injection pulses to control the duration of opening of fuel injection valve means.
2. Description of the Prior Art
Conventional electronic fuel injection control systems first determine a basic fuel injection signal pulse width Tp by deriving an air flow rate per engine rotation Q/N from the intake air flow rate Q measured with the use of an air flow meter and the engine rotational speed N detected in accordance with an ignition pulse signal or any other suitable signal proportional to engine rotational speed and multiplying the obtained value Q/N by a constant K and then calculate an effective fuel injection signal pulse width Te by performing an arithmetical operation expressed by the following equation: EQU Te=1/2.multidot.Tp.multidot.[1+(1+2W){1+2(S+R+D+F)}] (1)
wherein W is the correction factor determined by engine coolant temperature, S is the correction factor required during engine starting, R is the correction factor required in acceleration, D is the correction factor required in deceleration, and F is the correction factor required at high load conditions.
The resulting effective fuel injection signal pulse width Te may be modified in accordance with an air/fuel ratio control signal from an exhaust gas sensor and a correction factor determined by the voltage of a battery, and with the use of another arithmetical equation if associated with fuel-cut controller to cut fuel to the engine during deceleration.
It can be seen from equation (1) that the fuel injection control system is required to carry out a number of multiplications (6 multiplications including the multiplication of the constant K). Although such a calculation can be made with a relatively small delay so as not to arise any problem with the use of a wired logic computer adapted to perform multiplications concurrently, a long run time is required with the use of a stored program computer adapted to perform arithmetical operations with time sharing. Most of currently available microcomputers have no multiplier and require much time to perform multiplications. For example, the Motorola Inc., Model MC 6800 8-bit microcomputer requires about 200 .mu.s for a multiplication of 8-bits by 8-bits and about 800 .mu.s for a multiplication of 16-bits by 16-bits. Therefore, 1.2 to 4.8 ms is required for such 6 multiplications.
Recently, improved microcomputers have been developed which are endowed with improved multiplying performance to reduce the run time of multiplications. However, they are expensive and require a spaceconsuming IC. Additionally, they required much time to perform multiplications as compared with addition and substruct operations.
There is the possibility of increasing the speed of rotation of an engine near 7,000 to 8,000 rpm. If the engine is rotating at 8,000 rpm, it takes 7.5 ms for each rotation of the engine. Such fuel is injected in synchronism with rotation of the engine, a calculation is required within 7.5 ms. In view of this, the run time of 1.2 to 4.8 ms is too long. The control system performs other arithmetical operations other than multiplication and thus it is undesirable that much time is wasted for such multiplications. Furthermore, in case where spark timing control, exhaust gas recirculation rate control and other controls are performed simultaneously in a single microcomputer, the operations of the microcomputer is very complex and it is necessary to reduce the time required to perform such multiplications. In addition, it is desirable to reduce the time required for such calculations as small as possible so as to control the engine with new data and without less delay although much time is allowed for calculations if the engine is rotating at low speeds. Accordingly, the conventional equation is not suitable for electronic controlled fuel supply systems using a digital computer.
As can be seen by a study of equation (1), the various correction factors S, R, D and F are multiplied by the correction term (1+2W). The various correction factors are dependent upon coolant temperature and the term (1+2W) is not always suitable for them. The various correction factors should be set as a function of coolant temperature. Accordingly, complex and time-consuming operations are required to provide an optimum pulse width of fuel injection signal in case where equation (1) is adopted to various types of automotive vehicle and engine.